Not entirely appropriate language (6)
I believe the answer is:
german
'language' is the definition.
(German is a language)
'not entirely appropriate' is the wordplay.
'not entirely' means to remove the last letter (most but not all of the word).
'appropriate' becomes 'germane' (I've seen this before).
'germane' with its last letter removed is 'GERMAN'.
(Other definitions for german that I've seen before include "Helmut?" , "Hamburger, perhaps" , "Manger (anag.)" , "Nationality of citizen of Bonn" , "Middle European, for example" .)